Over the last two decades many products have been manufactured to contain a machine readable bar code. The bar code contains bars (areas which contrast with the optical background) of varying width representing a code number or alphanumeric description. A light beam is passed over the bar code and the reflection of the light beam is registered by a light detector whose output goes to a computing device. The latter converts the signal from the light detector into the code number or alphanumeric description represented by the varying width bars. Various different schemes are in widespread use for the representation of codes by varying width bars, and many of these schemes contain verification digits or characters. As well, various schemes are in widespread use for the reading of the bar codes. Some schemes use a stationary light source in a wand moved by the user while other schemes use a laser light source directed in many different directions each second automatically by rotating mirrors. Advanced schemes such as imaging the entire bar code `at once` (i.e., much as a video camera images a scene) and then using a computer program to enhance the image and then decode the image, have existed commercially for a number of years but are not yet in widespread use.
A major problem with bar codes is that they often cannot by read by the bar code reader. Occasionally the bar codes have been printed improperly and occasionally the bar codes have worn off. However, in the vast majority of modern products, the reason that the bar code cannot be read is because the bar code is covered with a foreign substance. A common problem in industrial environments is that dirt covers portions of the bar code. A common problem in supermarket retail environments is that water or ice has condensed over portions of the bar code.
One solution to dirty or occluded bar codes is to use a more powerful light source to read the bar code. A problem with this solution is that high amplitude concentrated light sources represent a danger to human sight. Another solution to dirty or occluded bar codes is for the operator of the bar code reader to somehow clean the bar code with an article of clothing, a piece of tissue or a piece of paper. However, the 10 to 15 seconds it takes to clean the bar code in such a fashion is significantly longer than the time it will take the operator to manually key into a keypad the product code typically printed beneath the bar code.
Bianco, U.S. Pat. No. 4,263,503, proposes a bar code label protection device. While such a device provides a solution to the prevention of dirty or occluded bar codes, such a device is not economical for use on inexpensive retail items.